This invention relates in general to electrophotography and more specifically, to an electrophotographic imaging member and process for using the imaging member.
In the art of electrophotography an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer a imaged by first uniformly electrostatically charging surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated, duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers such as an anti-curl backing layer and an overcoating layer. Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that the numerous layers limit the versatility of the multilayered belt photoreceptor. For example, there is a great need for long service life flexible photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptors belt systems fitted into a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of a photoreceptor belt after toner image transfer. Unfortunately, small diameter rollers, e.g less than about 0.75 inch (19 mm) diameter, raise the threshold of mechanical performance criteria to such a high level that spontaneous photoreceptor belt material failure becomes a frequent event for multilayered belt photoreceptors. Thus, in advanced imaging systems utilizing multilayered belt photoreceptors, cracking has has been encountered in one or more critical photoreceptor layers during belt cycling over small diameter rollers. Cracks developed in charge transport layers during cycling were manifested as print-out defects which adversely affected copy quality. Frequent photoreceptor cracking has a serious impact on the versatility of a photoreceptor and reduces the its practical value for automatic electrophotographic copiers, duplicators and printers.
Moreover, seams in multilayered belt photoreceptors tend to delaminate during extended cycling over small diameter support rollers. Seam delamination is further aggravated when the belt is employed in electrophotographic imaging system utilizing blade cleaning devices. In addition, belt delamination is encountered during web slitting operations to fabricate belt photoreceptors from wide webs. Alteration of materials in the various belt layers such as the conductive layer, blocking layer, adhesive layer, charge generating layer, and/or the charge transport layer to reduce delamination is not easily effected because the new materials may adversely affect the overall electrical, mechanical and other properties of the belt such as residual voltage, background, dark decay, flexibility and the like.
Moreover, the electrical cyclic stability of transport layers in multilayer structured photoreceptors has been found to be unstable when cycled thousands of times in liquid development systems. The carrier fluid of the liquid developer tends to leach out active small molecules, such as diamine compounds, present in the charge transport layers thereby altering the electrical characteristics of the photoreceptor. The leaching out of the active small molecule increases the susceptibility of the transport layer to solvent/stress cracking when the belt is parked over a belt support roller during periods of non-use. Some carrier fluids also promote crystallization of the active small molecules, such as diamine compounds, in the transport layers, particularly when high concentrations of the diamine compounds are present in the transport layer binder. Crystallization of active small molecules adversely alters the electrical and mechanical properties of a photoreceptor.
Photoreceptors having charge transport layers containing small molecule diamine compounds are well known in the art. Similarly, photoreceptors utilizing polyester adhesive layers are also known.